The present invention relates generally to the utilization of lignocellulosic biomass, and in certain embodiments to systems and processes useful for treating aqueous slurries of lignocellulosic biomass at elevated temperatures to render cellulose therein more susceptible to hydrolysis.
As further background, increasing emphasis has been placed in recent years upon finding ways to efficiently produce fuels from renewable, non-petroleum resources. In one field of interest, fuel ethanol has been produced by fermentation of biomass feedstocks derived from plants. Currently, fuel ethanol is commercially produced from feedstocks of cornstarch, sugar cane and sugar beets. These materials, however, find significant competing uses in the food industry, and their expanded use to make fuel ethanol is met with increased prices and disruption of other industries. Alternative fermentation feedstocks and viable technologies for their utilization are thus highly sought after.
Lignocellulosic biomass feedstocks are available in large quantities and are relatively inexpensive. Such feedstocks are available in the form of agricultural wastes such as corn stover, corn fiber, wheat straw, barley straw, oat straw, oat hulls, canola straw, soybean stover, grasses such as switch grass, miscanthus, cord grass, and reed canary grass, forestry wastes such as aspen wood and sawdust, and sugar processing residues such as bagasse and beet pulp. Cellulose from these feedstocks is converted to sugars, which are then fermented to produce the ethanol.
A difficulty in using lignocellulosic feedstocks is that the cellulose content of the biomass is caught up in a structure that inhibits the accessibility of the cellulose to agents that convert it to sugars. For this reason, research has focused upon methods for pretreating lignocellulosic biomass to enhance the susceptibility of the cellulose to conversion to sugars. Such pretreatment processes are designed to break the lignin seal protecting the cellulose and to disrupt the crystalline structure of the cellulose. A variety of pretreatment methodologies have been explored for this purpose; including physical processes such as size reduction, steam explosion, liquid hot water, irradiation, cryomilling, and freeze explosion; and chemical processes such as acid hydrolysis, buffered solvent pumping, alkali or alkali/H2O2 delignification, solvents, ammonia; and microbial or enzymatic methods.
Despite previous efforts relating to pretreatments for lignocellulosic biomass feedstocks and its ultimate use in the production of ethanol, needs remain for improved and alternative biomass pretreatment processes and follow-on production of ethanol. In certain of its aspects, the present invention is addressed to these needs.